I see three initiatives (official or not) important for D8 which desperately need help:

1. The mobile initiative (official) led by John Albin.
2. The project browser to solve / help a critical task: New users universally did NOT understand that you can extend Drupal. This would allow to browse modules and themes on drupal.org and install them on a site all from the Drupal UI.
3. Use Twig as our default theme engine. Most work is in this sandbox.